The present invention relates to optical communication techniques, more particularly, the present invention provides a delay line interferometer based on silicon photonics waveguides with polarization compensation at selective frequencies.
Over the last few decades, the use of communication networks has exploded. In the early days Internet, popular applications were limited to emails, bulletin board, and mostly informational and text-based web page surfing, and the amount of data transferred was relatively small. Today, Internet and mobile applications demand a huge amount of bandwidth for transferring photo, video, music, and other multimedia files. For example, a social network like Facebook processes more than 500 TB of data daily. With such high demands on data and data transfer, existing data communication systems need to be improved to address these needs.
40-Gbit/s and then 100-Gbit/s data rate dense-wavelength-division multiplexing (DWDM) optical transmission over existing single-mode fiber is a developing target for the next generation of fiber-optic communication networks. The big hang up so far has been the fiber impairments like chromatic dispersion that are slowing the communication signal down. Everything is okay up to 10 Gbits/s for distances less than 100 km and at 1300 nm transmission wavelength, but beyond that, distortion and attenuation take their toll. Many approaches are proposed on modulation methods for transmitting two or more bits per symbol so that higher communication rates can be achieved. Mach-Zehnder modulators can handle the higher data rates but require a driver that is differential with a wide output voltage swing. Beyond the light modulation for data transmission, the optical multiplexer (MUX) and de-multiplexer (DEMUX) of light signals is an essential building block for the optical network based on silicon photonics.
Silicon photonic devices can be made using existing semiconductor fabrication techniques, and because silicon-on-insulator is already used as the substrate for most integrated circuits, it is possible to create hybrid devices in which the optical and electronic components are integrated onto a single microchip. In particular, silicon photonic devices have been applied in WDM, e.g., CWDM or particularly DWDM, optical transmission networks, in which MUX/DEMUX wavelengths may be changed by environment temperature to cause problems to optical signals transmitted through the networks. A delay line interferometer (DLI) based on silicon photonics waveguides can be an important 2-channel MUX/DEMUX device with very low loss based on time-delayed two-beam interference in its two waveguide arms. However, for most given DLI device with two arms of a same material having a length difference ΔL, the group indices for TE and TM mode polarized light waves may be different due to birefringence effect of the waveguide material, causing different free spectral ranges for the TE mode and TM mode and resulting misaligned TE and TM passbands. Therefore, it is desired to develop silicon photonics based delay line interferometer with polarization compensation at selective passband wavelengths for WDM applications.